You need to do this twice, ideally with 4 to 6 hours between the times of the two readings. Record the position of the shadow of the gnomon's tip and the exact time and date. You can take the two readings on different days, as long as the clocks are consistent. If you take one reading in standard time and the other in daylight saving time (summer time) the results will be incorrect.
For each of the two shadow points, enter the date, time, and coordinates in the Calcad input box.
Important: the kind of hour, standard or daylight saving, must be the same for the 2 points.